Abstract: In order to improve the stability of robot variable polarity plasma arc (VPPA) welding process for aluminum alloy, a 600 A level full digital robot VPPA welding power supply based on advanced RISC machines (ARM) was developed. Double-inverter structure was adopted in the main circuit, while full-bridge inverter circuit topology was used in the primary inverter circuit, and the secondary inverter was with double-parallel-half-bridge inverter circuit structure. A STM32F405RGT6 ARM microprocessor with Cortex-M4 kernel was the main control chip with a FreeRTOS-embedded real-time operating system, and a full digital control system was designed. An adaptive fuzzy immune PID control algorithm was used to realize the closed-loop control of current, a stable current output waveform was obtained. A digital control panel based on ARM was designed to realize the digitization of humanmachine interaction. Both performance test and actual welding process test indicate that the developed robot VPPA welding power supply has excellent performance in dynamic adjustment, the welding process is stable and reliable with good weld formation.